Abstract.Sponges on subtidal red‐mangrove prop roots may become exposed to air many times per year during very low tides. Full exposure is stressful and potentially fatal, particularly if occurring in full sun. Large root sponges show distinct species zonation between mean low water and ‐0.5 m.Haliclona implexiformisandLissodendoryx isodictyalis arenear the top whileScopalina ruetzleriare near the lower end of the range. Temporary experimental desiccation resulted in 100 recovery of all three species after they had been exposed to either sun or shade for up to 2 h.Scopalinais the least resistant and lost over 90 tissue within 3 days after the 4‐h and 6‐h experiments; the remaining cell mass succumbed to infestation by microbes.HaliclonaandLissodendoryxrecovered from as much as 6 h in full sun but lost 85 and 80 of the original tissue volume, respectively. InLissodendoryx, clusters of larvae developed in the regenerating fragments. Water loss tolerated by the three species is estimated as 66 of wet weight inHaliclona, 54 inLissodendoryxand 38 inScopalina. Salinity of interstitial seawater (pore water) extracted from exposed sponges rose from ambient 3.5 to 4.348 after 1 h, to 5.1–5.9 after 6 h. Most endobionts died or left their host during this last phase. Natural vertical zonation in these sponges reflects their resistance to tidal
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